AB0883 IDIOPATHIC OPHTHALMIC MYOSITIS: CLINICAL PRESENTATION, THERAPEUTIC APPROACH AND IMAGING DIFFERENTIATION FROM GRAVES OPHTHALMOPATHY
Authors: S. Ziaragkali, O. Argyropoulou, G. Boutzios, S. Chatzi, E. Papadaki, A. Karantanas, A. Tzioufas, M. N. Manoussakis
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Idiopathic ophthalmic myositis (IOM) represents a rare autoimmune ophthalmoplegia of unknown etiology, that may mimic predominantly Graves' ophthalmopathy (GO). IOM is characterized by pronounced inflammatory infiltration of extraocular muscles leading to fibrosis and eye-threatening complications, if remains untreated [1,2]. The rarity and clinical heterogeneity of the disease pose diagnostic and therapeutic challenges. <h3>Objectives</h3> To describe the clinical phenotype, therapeutic interventions and clinical course of IOM and to define the distinct imaging features that differentiate IOM from GO. <h3>Methods</h3> This is a single-center, retrospective, observational study of 14 consecutive patients with IOM followed-up between 2017 and 2022. Cumulative clinical, laboratory and imaging data from the medical records until last follow-up were analyzed. The detailed orbital magnetic resonance (MRI) findings of 11 IOM patients were compared to those of 16 age- and sex-matched GO patients. <h3>Results</h3> IOM patients studied (men: 9/14, median age at disease onset: 46 years, median follow-up time: 15.5 months), presented subacute clinical course in 57%, whereas most common clinical manifestations were unilateral exophthalmos (79%), diplopia (71%), eyelid drop and/or swelling (50%). Extraocular muscle inflammation most commonly involved horizontal recti (median number of affected muscles: 2) and predominantly caused restrictive motility disturbance (71%). Anemia of chronic disease occurred in 36% of patients, however, erythrocyte sedimentation rate and c-reactive protein levels were found within normal limits. Myositis specific or other autoantibodies were not detected. Orbital MRI assessments revealed significantly more frequent occurrence of intraconal/extraconal fat edema (in at least one eye) in IOM patients (64.0%), compared to GO patients (25.0%, p-value 0.01). In addition, the abnormal contrast enhancement in extraocular muscles was present in 91.0% and 75.0% of IOM and GO patients, respectively, whereas tendon involvement was observed exclusively in IOM patients (18.2%). In all patients, the mainstay of therapy was steroids. IOM patients were treated with various combinations of corticosteroids and c-DMRD/b-DMRD (methotrexate, mycophenolate-mofetil, azathioprine, rituximab, tocilizumab), whereas GO patients mainly received corticosteroids with/or without tocilizumab. <h3>Conclusion</h3> IOM is a potentially severe organ-specific disease with heterogeneous clinical presentation. Early diagnosis and aggressive immunosuppressive treatment are required to prevent permanent eye-threatening complications. IOM should be considered in the differential diagnosis of exophthalmos, while MRI-imaging may help in differentiating IOM from GO. Studies are underway to delineate tissue-specific alterations of the inflamed extraocular muscles and involving larger series of patients. <h3>References</h3> [1]McNab A. Orbital Myositis: A Comprehensive Review and Reclassification. Ophthalmic Plast Reconstr Surg. 2020 [2]Montagnese F., Wenninger S. &amp; Schoser B. "Orbiting around" the orbital myositis: clinical features, differential diagnosis and therapy. <i>J Neurol</i> 2016. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.